The present invention relates to a soybean beverage base and food products prepared therefrom. More particularly, this invention relates to a soybean beverage base exhibiting enhanced nutritional quality, flavor, stability and palatability and to processes for the preparation thereof.
Soybeans have long been used as a well balanced source of nutrients for both animals and humans. In particular, soybeans are an excellent high protein, low carbohydrate source. Despite these nutritional credits, the use of soybeans, especially as a beverage base, has been quite limited principally because of the undesirable bean-like or "painty" flavor and odor heretofore associated with such beverages. Prior attempts to overcome this problem have been largely unsuccessful. The undesirable flavor and odor are principally caused by an enzyme system, lipoxidase, which catalyzes the oxidation of the polyunsaturated oils and fats in the soybeans. The reaction can take place quickly whenever: (1) the bean cell structure is damaged, as when the bean cotyledons are bruised, cracked or ground, so that the enzyme and oil are permitted to contact each other, and (2) a certain amount of water is present. As little as one part in one billion of the oxidized reaction product can be detected organoleptically and, for this reason, it is difficult and expensive to remove sufficient reaction product to impart a bland taste to the resulting beverage. Thus, it is extremely desirable to prevent the formation of such reaction product.
Soybean beverages, principally employed as a substitute for milk, have been prepared for hundreds of years, especially in the Orient, conventionally, by soaking soybeans in water for several hours, followed in order by grinding with water to thereby extract the protein into the aqueous phase, filtering the resulting slurry to recover the protein-rich extract and cooking the recovered filtrate. Although this process is simple and the resulting beverage is high in protein, the product has the distinct bean-like off-flavor and odor which has now become associated with soybean beverages.
It was subsequently found that various heating techniques such as boiling, steaming or infrared treatment of the beans could reduce the off-flavor of the soybean beverages. It soon was recognized, however, that although heating is necessary to reduce the undesirable bean-like flavor, it has the concomitant effect of insolubilizing or denaturing the protein, thereby substantially decreasing the protein concentration in the filtrate. Consequently, a compromise was effected wherein the heating operation was restricted, thereby retaining some of the bean-like off-flavor, in an effort to retain high protein concentration. This compromise has limited the acceptability of the resulting soybean beverages in the Western world and has confined its salability to such areas as animal feeds and non-allergenic milk substitutes for babies, which collectively form what might be considered a non-complaining market.
As diet consciousness sweeps across the Western world, high protein, low carbohydrate substitutes for milk and other dairy products have come into high demand. As opposed to the non-complaining market which heretofore consumed the bulk of the soybean beverages sold, diet consciousness is a problem generally associated with the adult population whose visual and taste requirements are quite sophisticated. This has resulted in extensive research and developmental efforts to develop a soybean beverage which can be sold as a stable suspension which will not separate on standing, thereby giving rise to the formation of "sludge" in the beverage container. Moreover, there has been great impetus toward significantly improving the palatability of the beverage with respect to taste, odor and mouth feel, i.e., a grainy or sandy feeling in the mouth and throat upon swallowing the beverage.
Recently, attempts have been made to prepare soybean beverages from whole soybeans without including an extraction step. In this manner, most of the nutritional components of the soybean are retained in the beverage, the product yield is higher and the labor costs are reduced. These attempts have been largely unsuccessful, resulting instead, in relatively unstable suspensions and poor flavor and mouth feel. Many attempts have been made to reduce the particle size of the solids in a soybean beverage in order to improve mouthfeel and stability since it was believed that poor mouthfeel and lack of stability of the dispersion were related to the presence of large particles remaining in the beverage. In some instances, the suspension has been centrifuged to separate and remove the larger, heavier particles. In other processes, size reduction has been effected through the use of hammer mills, roller mills, disc mills, disintegrators, and the like. Such size reduction apparatus has been used alone, in combination and in further combination with homogenizing and/or emulsifying apparatus. Nevertheless, permanently stable suspensions have still not been obtained. In many instances, suspending agents or suspension stabilizers are still required. Moreover, none of these techniques have provided a whole soybean product which combines the features of (1) being essentially free of the bean-like or painty, off-flavor normally associated with soybean beverages; (2) maintaining a permanently stable suspension; and (3) exhibiting good mouthfeel.
U.S. Pat. No. 3,901,978 discloses a successful process for preparing a bland, stable aqueous dispersion of whole soybeans comprising:
i. tenderizing intact soybean cotyledons until the soybeans exhibit a tenderometer value of between about 16 and about 300 pounds/100 gms. of soybeans; PA1 ii. heating the intact soybean cotyledons sufficiently to inactivate the lipoxidase enzyme; PA1 iii. forming a slurry of the soybeans and water, said slurry having a soybean concentration of less than about 20 percent by weight; PA1 iv. homogenizing said slurry in at least one pass through a homogenization zone at a pressure between about 1000 and 10,000 psi. at a temperature between about 32.degree. F. and the boiling point of the slurry at the pressure within the homogenizing zone; and, PA1 v. recovering a bland, stable aqueous dispersion of whole soybeans. PA1 i. heating soybean cotyledons either intact or in sub-divided form, sufficiently to inactivate the lipoxidase enzyme contained therein and to partially tenderize said soybean cotyledons; PA1 ii. further tenderizing said soybean cotyledons until the soybeans exhibit a tenderometer value of between about 16 and about 300 pounds per 100 grams of soybeans on an equivalent whole bean basis; and PA1 iii. homogenizing an aqueous slurry of 11.4tenderized soybeans, said slurry having a soybean concentration of less than about 20% by weight, in at least one pass through a homogenization zone at a pressure between about 100 and 10,000 psi. at a temperature between about 32.degree. F. and the boiling point of the slurry at the pressure within the homogenizing zone, thereby obtaining a bland, stable soybean dispersion.
At the present time, the reasons for the clear superiority of the soybean beverages prepared in accordance with said copending application as compared to the prior art are not completely understood; however, while not wishing to be bound by any proposed theory or mechanism, it is currently believed that the combination of a specific amount of tenderization and a commensurate amount of homogenization results in the formation of hydrophilic lipid-protein complexes which enable the soybean dispersion to remain stable, with no appreciable separation, for over two months. Soybean protein is normally quite hydrophobic. This leads to protein aggregation causing precipitation of the resultant relatively heavy particles. Colloidal stability of a soybean beverage can be defined as the continued maintenance of a homogeneous liquid system, i.e. the absence of the separation, either settling or floating, of the solids within the liquid. The system is not, in fact, a true colloidal system because the particle size of the solids exceeds the range normally considered as being within the colloidal size range. Thus, contrary to the prior art concern for the obtainment of small particle size as a prerequisite for good stability and mouthfeel, it is now believed that hydration of the protein renders it more hydrophilic thereby enabling prolonged suspension thereof. Tenderization of the soybean cotyledon in accordance with said copending application is believed to effect a desirable hydration of the molecular constituents of the soybean, e.g., the proteins, carbohydrates, combinations thereof, etc. Thus, upon tenderization, the soybean protein becomes more amenable to subsequent phospholipid-protein complex formation during homogenization. The resulting complex is believed to comprise a protein particle enveloping a core of soybean oil with hydrophilic moieties of phospholipid molecules emanating from the protein particle, said hydrophilic phospholipid moieties tending to create a water sheath about the protein in the aqueous dispersion, thereby imparting a hydrophilic character to the resulting complex. Moreover, because of the soybean oil core, the resulting complex exhibits less density than normal protein particles, thereby assisting in avoiding settling and maintaining the stability of the suspension.
In U.S. Pat. No. 3,901,978, it is disclosed that the soybean cotyledons should be retained intact, i.e., retain their structural integrity (although dehulling in a manner which retains the structural integrity of the cotyledon is specifically contemplated in said copending application), until at least that point in the process wherein the lipoxidase enzyme has been inactivated. It has now been found that under certain conditions, the soybean cotyledons need not be processed in an intact condition, thereby enhancing the flexibility and applicability of the process. Also, it has now been found that the process can be further modified to increase the nutritional value of the resulting soybean beverage while simultaneously effecting a substantial reduction in waste pollution.